Raman and infrared spectroscopy, DFT calculations, and vibrational assignment of the anticancer agent picoplatin: performance of long-range corrected/hybrid functionals for a platinum(II) complex.

Picoplatin, cis-[PtCl2(NH3)(2-picoline)], is a new promising anticancer agent undergoing clinical trials, which reveals high efficacy against many tumors and greatly reduced toxicity, in comparison to cisplatin. In this work, we present for the first time the Fourier-transform Raman and infrared spectra of picoplatin, in the region of 3500-50 cm(-1). The comprehensive theoretical studies on the molecular structure, the nature of Pt-ligand bonding, vibrational frequencies, and intensities were performed by employing different DFT methods, including hybrid (PBE0, mPW1PW, and B3LYP) and long-range-corrected hybrid density functionals (LC-ωPBE, CAM-B3LYP). Various effective core potentials (ECP) and basis sets have been used. In the prediction of the molecular structure of picoplatin, the best results have been obtained by LC-ωPBE, followed by PBE0, mPW1PW, and CAM-B3LYP density functionals, while the least accurate is B3LYP. The use of the LanL2TZ(f) ECP/basis set for Pt, in conjunction with all tested DFT methods, improves the calculated geometry of the title complex. The PBE0, mPW1PW, and CAM-B3LYP methods have shown the best performance in the calculations of the frequencies of Pt-ligand vibrations. A clear-cut assignment of all the bands in the IR and Raman spectra have been made on the basis of the calculated potential energy distribution (PED). The nature of the "vibrational signatures" of picoplatin have been determined. These results are indispensable for further investigation on drug-target interactions using vibrational spectroscopy.